1. Field of the Invention
The present invention relates to a method of communicating using a mobile terminal, and more particularly, to a method and apparatus for communication of a mobile terminal by using a relay device.
2. Related Art
Advances in wireless communication technologies have triggered a need to continue communication while walking or moving via a vehicle, rather than simply communicating using a mobile terminal. One of the most important technical aspects of communicating during movement is seamless access to a distributed network such as the Internet.
In particular, research has been actively conducted into a method of continuously receiving Internet services by establishing a seamless connection between various types of network equipments. Even if during data communication, a mobile terminal not only moves within a network but also moves from one network to another network, handover must be efficient to continuously maintain seamless communication.
For a fast handover, which is the core part of research into handover techniques, “layer2 (L2) information” or information called “L2 trigger information” needs to be obtained from a network equipment. However, as types of wireless network equipments have increased and a tendency toward compact mobile terminals has spread, it is difficult to include all network equipments into a single mobile terminal.
In addition, as networking equipment can be installed in various types of vehicles, thus allowing a mobile terminal to receive networking services, a reconnection between the network equipment and the mobile terminal, that is, a connection between the network equipment and the mobile terminal in a cascade fashion via a relay device, has gradually increased.
Since wireless network equipment is basically installed in a mobile terminal that can be connected to a vehicle in a cascade fashion, via wire or wirelessly, the mobile terminal may establish connection, via not only a relay device but also wireless networking equipment included in the mobile terminal. Thus, a handover needs to be performed between the mobile terminal and the network equipment.
However, if the relay device and the mobile terminal are connected via wire, wired networking equipment does not have a function of providing L2 trigger information and thus cannot perform a fast handover. Conversely, if the relay device and the mobile terminal are connected wirelessly, the mobile terminal is not capable of determining whether a communication environment between the relay device and a base station changes and thus also cannot perform a fast handover.
FIG. 1A is a diagram illustrating an example of a conventional communication apparatus using a relay device. Referring to FIG. 1A, the conventional communication apparatus includes a base station 112, a relay device 114, and a mobile terminal 116 that is connected to the relay device 114, via wire.
The base station 112 communicates with the mobile terminal 116, via the relay device 114. The relay device 114 receives a signal from the base station 112, via a wireless network, and transmits the signal received from the base station 112 to the mobile terminal 116. The relay device 114 can be installed in various types of movable platforms, e.g., a movable platform 119, such as, for example, an automobile, a plane, or a ship that is moving from one service area to another service area within the wireless network or between different wireless networks. In the current embodiment, the relay device 114 is installed at a particular location of a movable platform 119 (vehicle), and then communicates with the base station 112 wirelessly, via a wireless network, and then communicates with the mobile terminal 116, via wire.
A wireless network module including an antenna is installed at a side of the relay device 114 in order to communicate with the base station 112, via a wireless network. In addition, the relay device 114 includes a wired network interface in order to communicate with the mobile terminal 116, via a wireless network. In an example embodiment, a network via the Ethernet is used as a wired network.
The mobile terminal 116 includes a wired network interface in order to communicate with the relay device 114, and the wired network interface is connected to the wired network interface of the relay device 114. In addition to the wired network interface, the mobile terminal 116 includes at least one of a plurality of wireless network interfaces, such as, for example, a wireless local area network (LAN), CDMA (Code Division Multiple Access), HSDPA (High Speed Downlink Packet Access) and WiBro (Wireless Broadband Internet) to communicate with the base station 112, via the relay device 114.
A connector for interfacing, which is connected to an end of an unshielded twisted pair (UTP) cable that is a part of the Ethernet, is connected to a mobile terminal 116 in order to allow the mobile terminal 116 to use networking, via the Ethernet. If the connector connected to the UTP cable is separated from the mobile terminal 116, the mobile terminal 116 cannot use the networking function of the Ethernet any longer. Thus, an Ethernet module included in the mobile terminal 116 connected to the relay device 114, via wire, can determine only whether the Ethernet is available by checking whether the connector is connected to the mobile terminal 116.
Since wired networking basically operates in a fixed mode, unlike wireless networking, no method has been introduced to solve a problem that the intensity of signal becomes weak in inverse proportion to the distance between the base station 112 and the mobile terminal 114. This is because wired networking can use another relay device even if the intensity of a signal becomes weak since the distance between the relay device 114 and the mobile terminal 116 is great when wired networking operates in the fixed mode.
However, if the relay device 114 leaves a service region of the base station 112 due to movement of a movable platform 119, i.e., a vehicle, wireless networking may not be performed between the relay device 114 and the base station 112. In this case, the mobile terminal 116 connected to the relay device 114, via wire, cannot access the Internet.
Communication is established between the relay device 114 and the mobile terminal 116 by using wired networking within the movable platform 119, i.e., a vehicle. However, it is impossible to determine whether the state of wireless networking between the relay device 114 and the base station 112 is good, unless the UTP cable is separated from the mobile terminal 116. Accordingly, the mobile terminal 116 cannot rapidly perform a handover from the Ethernet to another communication environment, such as, HSDPA, CDMA or WiBro.
Handover is a technique in which the Internet can be seamlessly accessed when the mobile terminal 116 moves from one service region to another service region.
For example, it is assumed that networking services are received, via a terminal device, in which all various types of wireless network equipments (wireless LAN, CDMA, HSDPA, etc.) are installed. In this case, services are received in a wireless LAN service region, via a wireless LAN; however, if the mobile terminal 116 leaves the wireless LAN service region, Internet services can be seamlessly received using HSDPA or CDMA in which the speed of data transmission is low and services are provided at high cost although the range of the service region is large. Such a technique is called “handover”.
In order to reduce occurrences of a disconnection phenomenon during a handover, it is necessary to receive information indicating whether the mobile terminal 116 leaves the service region of the base station 112, which is referred to as the L2 information or L2 trigger.
Wireless communication may be established by reconnecting a mobile terminal 116 to a base station 112, via a relay device, rather than by directly connecting the mobile terminal 116 to the base station 112. The quality of wireless communication using even the same wireless technology depends on whether the mobile terminal 116 is connected to the base station 112 directly, or via a relay device 114, such as an antenna for vehicles. In particular, in the case of a ship or a plane, a wireless Internet service cannot be provided, via direct connection, to the base station 112, and thus, reconnection needs to be performed, via the relay device 114.
Thus, the relay device 114 is installed in a movable platform 119, such as, an automobile. However, if the relay device 114 leaves a service region of the base station 112 due to movement of the movable platform 119, the mobile terminal 116 cannot receive a service under such a communication environment. Thus, a handover must be performed to another communication environment that is available to the mobile terminal 116. However, in the case of networking via the relay device 114, the L2 trigger information is not transmitted to the mobile terminal 116, thus preventing a fast handover from being performed.
FIG. 1B is a diagram illustrating another example of a conventional communication apparatus using a relay device. Referring to FIG. 1B, the conventional communication apparatus includes a base station 122, a relay device 124, and a mobile terminal 126 that is wirelessly connected to the relay device 124.
The base station 122 communicates with the mobile terminal 126, via the relay device 124. The relay device 124 receives a signal from the base station 122, via a wireless network, and transmits the signal received from the base station 122 to the mobile terminal 126. The relay device 124 can also be installed at a movable platform 129, such as, for example, an automobile, a plane, or a ship that is moving from one service area to another service area within the wireless network or between different wireless networks. The relay device 124 includes a wireless network module including an antenna installed at one side of the relay device 124 in order to communicate with the base station 122, and a wireless network interface arranged in order to communicate with the mobile terminal 126.
The mobile terminal 126 includes a wireless network interface for communicating with the relay device 124. In addition to the wireless network interface to communicate with the relay device 124, the mobile terminal 126 also includes at least two of a plurality of wireless interfaces, such as CDMA, HSDPA, and WiBro, to communicate with the base station 122, via the relay device 124.
The conventional communication apparatus illustrated in FIG. 1B is the same as the conventional communication apparatus illustrated in FIG. 1A, except that the relay device 124 and the mobile terminal 126 are connected via a wireless network rather than via a wired network.
Even if the mobile terminal 126 is wirelessly connected to the relay device 124, the quality of communication is always satisfactory irrespective of whether communication is seamlessly established between the relay device 124 and the base station 122. This is because the mobile terminal 126 is capable of determining a communication environment by using, for example, a beacon signal, which is received from the relay device 124. However, the mobile terminal 126 cannot detect the state of communication between the relay device 124 and the base station 122.
Accordingly, the mobile terminal 126 cannot perform a fast handover. That is, the mobile terminal 126 cannot perform a handover until communication is completely discontinued between the relay device 124 and the base station 122 and, thus, undergoes a discontinuity in communication for a significantly long period of time.
As described in connection with FIGS. 1A-1B, in a conventional communication apparatus using a relay device, a mobile terminal is not capable of determining whether a communication environment between the relay device and a base station changes and, thus, cannot perform a fast handover.